1. Field of the Invention
The present invention relates to a writing method of an optical disc drive, and more particularly, to a writing method of adjusting writing power to ensure writing quality when the optical disc drive switches the data transfer rate.
2. Description of the Prior Art
For a writable optical disc, a laser beam from a pick up head is projected onto the optical disc to burn marks (e.g., a cave or a deformation) of different lengths according to the writing power of the laser beam. A difference in reflection lights between locations with marks and without marks is utilized to form digital signals to document data.
As shown in FIG. 1, which is a writing method of a conventional optical disc drive, a spindle motor 1 rotates an optical disc 2, a pick up head 3 is moved along a radial direction of the optical disc 2, and the pick up head 3 projects a laser beam onto the optical disc 2. Since inner tracks and outer tracks of the moving disc 2 have different moving speeds, the optical disc 2 is divided into a plurality of areas of different data transfer rates from inner tracks to outer tracks, and the data transfer rate is changed gradually from low to high, for example, from 2×, 4×, 6× to 8×, etc., to enhance data transfer efficiency.
Since the optical disc 2 can be produced by many manufacturers, the materials, components and manufacturing procedures in usage may be different and the optical disc 2 may have different reaction sensitivities to the laser beam. The optical disc 2 stores recommended writing power, write strategies and quality parameters (i.e., a beta parameter) for all kinds of data transfer rates in the lead-in area 4; however, the outcome may still be different due to individual differences between different kinds of optical disc drives. Therefore, a power test area is further allocated within the lead-in area 4 of the optical disc 2 for performing a practical writing test in the neighborhood of the recommended writing power during low data transfer rate 2×. Burned marks are read out after the test, reflection lights are referred to, and decoding correctness and signal intensity etc. are determined, to calculate a beta parameter for evaluating the burned marks. The recommended beta parameter is utilized as a target to choose a corresponding writing power as the optimized writing power of the optical disc, and to complete an optimum power control (OPC) test. The optimum power control at low data transfer rate 2× cannot be directly used, so the OPC test result at low data transfer rate 2× should be utilized to estimate writing powers of high data transfer rates according to past experience.
A problem with estimating writing power according to past experience is that the writing power at high data transfer rates has a great variation and therefore it is hard to maintain a stable writing quality for the optical disc. Prior art R.O.C. Patent No. I276083 utilizes the OPC test result of low data transfer rate 2× to perform a writing operation directly, and simultaneously monitors the beta parameter when writing to compensate the writing power according to experience to achieve the target beta parameter. The writing power and the compensation value of each high data transfer rate cannot be correctly obtained, however, and therefore the beta parameter cannot quickly converge to the target value. Another prior art, R.O.C. publication No. 200917233, performs actual writing experiments at different data transfer rates; however, the storage capacity of the optical disc will be reduced if all the test areas are to be allocated in each high data transfer area. Besides, test data and test modes of each high data transfer rate must be prepared and transferred, meaning normal writing operation will be interrupted, so a longer time is required for writing and the writing efficiency is degraded. Therefore, the conventional writing method of optical disc drives still has issues concerning adjusting writing powers between high data transfer rate and low data transfer rate.